Automatic switching system.



E. H. CLARK. AUTOMATIC SWITCHING SYSTEM. APPLIQATION FILED JAN. 20, 1908.

' Patented M1126, 1915.

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APPLICATION TILED JAN. 20. 1908.

Patented Jan. 26, 1915.

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E. H. CLARK. AUTOMATIC SWITCHING SYSTEM.

APPLICATION FILED JAN.20, 1908.

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AUTOMATIC SWITCHING SYSTEM.

APPLICATION FILED J'AN.20,1908

Patented Jan. 26, 1915.

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E. H. CLARK. AUTOMATIC SWITCHING SYSTEM. APPLICATION FILED JAN.20, 1908.

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E. H. CLARK. AUTOMATIC SWITCHING SYSTEM. A'PPLICATION FILI 1D JAN. 20,1908:

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EDGAR H. CLARK, 01? AUSTIN, ILLINOIS, ASSIQNOR, BY DIRECT AND MESNE ASSIGN- MENTS, TOWESTERN ELECTRIC COMPANY, OF NEW YORK, N. Y., A CORPORATION on ILLINOIS.

AUTOMATIC SWITCHING SYSTEM.

Specification of Letters Patent.

Patented Jan. 26, I9]! 5..

Application filed January 20, 1908. Serial No. 411,669.

To all whom. it may concern Be it known that I, EDGAR H. CLARK, a citizen of the United States of America, and a resident of Austin, county of Cook, and State of Illinois, have invented a new and useful Improvement in Automatic Switching Systems, of which the following is a specification.

My invention pertains to switch systems suitable for telephone exchanges and its ultimate object is the economy of line conduc'tors.

It relates particularly to telephone systems wherein one or more main ofii ces are supplemented by one or more outlying offices, or sub-oifices, in which groups of subscribers lines center and between which and the main, office or oflices trunk lines extend. I

I have. chosen particularly to illustrate my invention as applied to a telephone system employing manually operated switch boards at its main switching center or centers, but obviously it may' be applied to other than manual systems. i

In connection with a manual switchboard I provide an outlying distribution point from which I cause to radiate short subscribers lines. 011 the manual switchboard at the main or central oiiice I provide calling and answering jacks and line signals. in short, a complete manual switchboard line equipment at the central oflice for each of the subscribers lines radiating from the outlying distribution point. Between the I outlying distribution point and the .inanual switchboard I provide. a system of auto matically operatlng trunk circuits and switches, the trunks bcing fe wer in number than the number of subscribers lines ra diating from the outlying distribution point and the operation of the switches being such that, when the. switching conditions of the telephone exchange as a whole require that any one of the outlying radiating subscribers lines connected through a trunk circuit with its set of switchboard ap pa ratus, that connection is made and main tained automatically by the trunk circuits and apparatus, and is automatically disconnected when the necessity for its maintenance no longer exists.

In the drawings, trunks are shown of two classes, first for connecting a calling line subscribefs line extending troni an outlying distribution point; and the circuits of the alternative end of the trunkof Fig. 2 Fig. t shows the circuits of the central office line equipment shown in Fig. 2; and the circuits of the central ofiice end of a trunk which connects a central office line equipment to its corresponding subscribers line extending from the outlying distribution'point, when a plug is inserted in a switchboard jack of the line equipment; Fig. 5 shows the circuits of the subscribers line shown in Fig. 3; and the circuits of the alternative end of the trunk of Fig. 4; Figs. 6, 7 and 8 show mechanical details of the autou'iatic switches in which the trunk circuits terminate both at the central office and at the outlying distribution point, Fig. 6 being a general figure, Fig. 7 a view of the off-normal switch in the direction of the arrow M, and Fig. 8 being view of wiper l2 and springs 20, section of wiper shaft 6 being taken on tlie line NY in the. direction shown by the arrow N.

In Fig. 6 are shown details of an automatic switch similar in most details to the well-known Strowger switch. The detcnt pawl is normally cut out of contact with the ratchet 2 and rack 3; when the release relay 4 is energized, detent pawl 1 is permitted to drop into contact with ratchet 1 11 116 t o, ts switchboard equipment. I The opj eratio'n is as follows Assume that substation presses one'pair and only one pair into contact when in any one of its'positions except the-normal position of rest, in which-position it is shown in the drawing. The onnormal switch 1314.-15 has its spring 14:

held against its spring 15 by leaf 16 on wiper shaft 6, the spring 14: being released i at-the first rotary step of wiper shaft 6.

F igs. 2 and 3 together show a complete,

circuit of a trunk for connecting a calling '56 calls, removing the receiver from the hook,,thus closing the line circuit, and assume that the directory number of this substation is 56 ,-or .156, or some directory mainingportionsof the directory number, Upon the closing ofv I the circuit of the line at substation 56, cur-' rent flows-from battery B .through 17 19,

' identify the group.

" number in which 56 identifies the position of the'substation56 in a group and the re- 56, 18 17 energizing subscribers primary line relay l7 and closing path for current; through B, subscribers secondary-line. re-

30. Relay 30 v closes path. or current through B release relay 4, i, 4", 80, 81', 82, 83, 33, 34;, 35, 30', earth, energizing release relay 4, by the closure of Whose armature" 4 path is'closed for current through B release relay 4, 77 and earth. By closure of armature 4 contact spring 4' is broken from contact 4 and connected to 4 thereby providing a path for continuing the energization of 4; independently of the ofinormal switch Sh -e82. Relay 30 also closes a path for pulsations of current through B interrupter I, 32, vertical magnet 5 of the automatic switch ofFig, 3 (corresponding to 5 of Fig. 6) ,3 3,34,35, 30, earth, and by each pulsation vertical magnet 5 is energized, lifting the wiper shaft 6 one step; 5 also closes its electrical arma-V ture contact and completes path for current throughB, 5 36, 15", 1d, 37 38, 39, earth, thereby (by the energization of vertical magnet 5 of the automatic switch in Fig. 2) stepping the wiper shaft 6 of Fig. 2 up the number of steps equal to the steps taken by the wipershaft 6; thus the Wipershafts 6 and 6 belongingto the two ends of the same trunk, which may be designated trunk ,A, containing conductors 38 and 46, move vertically substantially in unison. The step-by-step movement of the shaft 6 moves the wiper l2 over the springs 21, etc., until the fifth pair of springs 25 (corresponding to the first digit of the directory number of the substation'56) is closed, when a path is formed for current through B, 40, 32, 32", 41, 25 ,12, 30,earth, energizing the first pilot switch or relay- 32; the relay 32, by its armature 32', interrupts the pulsating circuit above traced through vertical magnet 5; by

lay 30, and resistance 31, energizing relay 53 and holding it energiz armahutlil loclrs'itself over the I ath B, 4:0, 320. 32!! 51 e y i armature 32, at closes pti h'z-ifll pu i ns of. current throughigBf vI, 44,1341, rotary ma et E 32 33, 34: $35,361 earth, and by .eac pulsation rotary magnet 7 is energized,;rotat1ng the wiper shaft 6' one step;

also. closes its electrical armature contact andcompletes-path for current through B j7{*,"45,-'i6,47,earth, thereby (by the combinatlon of rotary magnet "I of the switch of Fig.v 2) stepping the wiper shaft '6 around the-number of steps equal to the number of steps taken by the wiper shaft 6; thus the wiper shafts 6 and 6 belonging tothe two ends of the trunk A, move in rotary motion substantially in unison. The

its armature 3l', it switches conductor 35 from conductor 33 to conductor 51, the import of which will'be discussed later; by its armature 34 it completespath' for current through B, 40, home trunk-e rtensionrelay 53, 54, 34, 52," earth, energizing relay d'' of its armature'34", 3-ii-"""ha s'" een' broken from 34, and 34? has made'contact with 34, thus connecting the'winding of relay 4 to wiper- 10F, thr0ugh 4, 4", 4 33', 339, 134, '10", thence to 56 ,50, 31,1and dlfllif'Bat tery; b the connectidm'of 111 0 fires-1'5.

ance re ay 4 to resistancoz-s 31, theliigh-re sistance secondary line-relay 30Zi shunted y movement out and releases its armature SQfftliis re moves the earth connection fi'oin' c'o'nductor 35, which is common to all lines of the group to-'which substation 56 belongs, and from conductor 41, which is common ,to'all lines on the fifth level of the bank of contacts of the automatic switch of Fig. 3.

,The switching of" conductor 35 from conductor 33 to conductor 51 is for the following purpose :The operating magnets 4, 5 and 7} of the'switch of the trunk A are normall connected the conductor 33, and, when t e trunk A is idle, are connected through armature 34 to conductor35; when the trunk A is busy (as is now considered to be the case because of the calling of sub station 56), the armature 34 dlSCOIlIlGOtS' those operating magnets and extends the trunk B may receive and respond to the next call originating in the group to which substation 56 belongs. and when trunlrB has responded properly to the second call from the group, trunk A remaining busy,

the operation of pilot relay-34: will extend common conductor through conductor 51 to the operating magnets o'ttrunk C, and so on throughout vall trunks of the group of trunks serving the group of lines. By the first rotary step of; wiper shaft 6, switch spring M was released, breaking contactfrom spring 15 and making contact with spring 13 By energization of home trunk-extension relay 53, the, trunk conductors are extended to the calling substation, and path is closed for current through B, 17 56, 8, contact of 53 38,

37, 14 13 55, contacts of relay 45 helix of 45 earth, retaining the .energization of relay 1? and energizing distant trunk-extension relay 45'*, which then locks itself through 13 contact-t i 57, resistance 58, 45", 45 earth. By the energization of relay 45*, the trunk conductors are extended to the line jacks corresponding to the calling substation and path is closed for current through battery 13*, line-signal-relay 56 60. (31. 56. 9 62. 16, contact of 53, 9,

'56, 1s, 56. 19, 56, e contact of 53 38,

contact of 45 63-, 8 56 6%, 65, 60", earth, energizing relay 56 and resulting in the glowing of line lamp L. A branch circuit exists from conductor 18 through winding 17. but the resistance of winding 1'7 shall be high enough to render its current negligible, 12,000 ohms being the resistance commonly used under such circumstances. In response to the lighting of the line lamp L, the operator in charge inserts the plug P into the jack J, thus completing a talking circuit through '13, repeating. coil winding 66, supervisory relay 67, 68, P, J, 61, 56, 9 62, 46, contact of 53 9*, 56, 18, 56, 1.9, 56, 8 contact of 53, 38, contact of 45 63, 8 56 64, J, P, 69, repeating coil winding 70. The subscribers hook switch controls the supervisory relay 67 in the usual manner. By the insertion of the plug P, path is completed also for current through B 71, 7'2. 73, 7%, J, 60, earth. energizing cutoff relay 60 and extinguishing lamp L in the usual manner. The energization of relay 60 connects earth to the resistance 75 in series with relay 56 and the battery B but relay 56 is not energized because of the path existing from battery B directly to the resistance 7 through armature 45 76, 10 56 to 75; as the batteries are the same or similar, the relay 56 has no potential difference at its terminals. The call is completed by the telephone operator in the usual manner. This completes the operation of setting up of a connection for a call originating at substation 56, or any substation served by a trunk such as A. It may be noted that the connection through the trunk A thus set up is not under the control of the originating substation, that substation controlling only the supervisory relay 67 and lamp 74. All the energizedrelays oi the trunk A are held energized through the armature 17, or through contacts which ultimately are held through armature 17, but

armature 17. is not under control of the substation 56 so long as plug P is in jack J, because of the circuit B, 17 56, 8, contact of 53, 38, contact of +L5 63, 8 56 64, J, P, 69, 70,'earth. Therefore, after the hanging up of the receiver at substation 56, the trunk A is held by the plug P until disconnection by the operator.

In disconnecting, when the circuit is broken at the substation and the operators plug has been removed, the relay 17 is deenergized; the armature 17' then releases the relay 4:, whose armature then releases relay 4. By the release of relays :t and r, all circuits and mechanisms are permitted to be restored to the normal condition of idleness, such restoration being completed by the final closing of the oii-iiormal The final step of restoration thus closes the circuit of 4 through S and 83, which is the first circuit used in the normal operation of the device; thus conr plete mechanical restoration is compelled before the device may begin its response to the next succeeding call.

Trunks per Figs. 2-3.;1nd Figs. 44 may be equipped with switches such as shown in Fig. 6. the springs 21. etc. of the switches of Figs. 2 and 5 being unconnected or omitted. and the switch 13-1l-15 ot' the switches of Figs. 3 and 4 being unconnected or omitted. The trunks are of two classeS.--thc first class for connecting an outlying sub scribers line to its switchboard line cqui ment when a substation originates a call.

. and the second class for connecting a switchboard line equipment to its outlying sulr scribers line when a call for the substation is originated elsewhere. A trunk ol the first class is shown in 2-3 and has beendescribed above. A trunk of the ond class is shown in Figs. 45. The central office line equipment oi the line or SllllSlir tion 56 is shown in Fig. 2 and also in Fig. 4, while the subscribers line and substation 56 and its primary and secondary line relays 17 and 30 are shown in Fig. 3 and also in Fig. 5.

The operation of a trunk of the second class, as shown in Figs. 45, is as follows:

Assume that a call has originated u on the switchboard for the substation 56. he operator in charge of the plug P of Fig. 1,

desiring to connect with the substation 56 by means of the plug P, inserts the plug P into the jack'J or into any of the multiple jacks ofthe switchboard line J equipment, and the-following automatic action takes place: Upon'the insertion of the plug P, current flows through B", 71, 72, 73 74, P, J, (30, earth, energizing the cut-off rela (;()*\\'hioh, by its armature 60", closes pat for current through battery B, secondary switchboard relay 56 resistance 75, 60",.

earth, energizing the secondary switchboard relay 56 and attracting its armature 130. Relay 56 closes path for current through B release relay 4*, 104, 104", 130, 81 82 183, 133, 134., 135, 130', earth, energizing release relay 4*, by the closing of whose armature 104 'path is closed for current through B, release relay 4, 177

and earth. By closure of armature 104 contact spring 101- is broken from contact 104 and connected to 104 thereby providing pathforcontinuing the energization of 4 independently of the off-normal switch SI -82. I Relay 56 also closes a path for pulsations ofcurrent through E, interrupter I, 132, vertical magnet 5 '0f the automatic switch of Fig. 4 (corresponding t0'5 of Fig. 6) 133, 131', 135, 130', earth, and by each pulsation vertical magnet 5? is energized lifting the wiper shaft 6 one step; 5 also closes its electrical armature contact and completes path for current through B", 5 13c, 15 11 .137, 138, 139, earth, thereby (by the energization of vertical magnet 5 of the automatic switch of Fig. 5) stepping the wiper shaft 6' of Fig. 5 up the number of steps equal to thesteps taken by the wiper shaft 6; thus the wiper shafts (3 and 6 belonging to the two ends of the same trunk, which may be designated trunk R, containing conductors 138 and 146, more vertically, substantially in unison. The step-by-step movement of the shaft 6 moves, the wiper 12 over the springs 21 etc. until the fifth air of springs 25 (corresponding to the rst digit of the directory number of the desired line) is closed, when a path is formed for current through B 140, 32*,132, 141, 25, 142, 130', earth, energii'ing the first 'pilot switch or relay 32 'relay 32?, by its armature 132, inter-.

rupts the pulsating circuit above traced through vertical magnet 5*; by its armature 132 ,.it locks itself over the path B 110, 322*, 132",132 143, contact, 101 earth; by its armature 132* it closes path for pulsations of current through E, I, 144, 134,'rotary magnet-7 132", 133, 134,- 135, 130, earth, and byeach puisation rotary magnet 7 is energized, rotating the wiper, shaft 6 one step; 7*,also closes its electrical armature contact and completes path for current throughB", 7?, .145',.146,

rotary m'a'gnet'Z of the switch of Fig. 5) stepping the wip'ej'r shaft 6 around the num-f 147, earth, thereby (by the energizations of Y ber of steps equal to the steps taken bythe wiper shaft .6; thus the wiper shafts 6 and 6 belonging to the two ends of the trunk R- move in rotary motion substan tiallyin 1;l n ison v p The step-by-step rotary movement of the shaft 6* moves the wiper 11 over the contact pieces of the-fifth level of contacts in the contact bank of the switch until contact piece 156 (corresponding to the second digit of the directory number of the line .de-

sired) is reached, when path is completed for current through B, 140, 34 134 11*, 156 149, 130, earth, energizingthe second pilot switch or relay 34; the relay 34 by .its armature 134",-interrupts the pulsating circuit path traced throughthe rotary magnet 7; byits armature 134, it locks itself over the circuit B 140, 34 134, 134*,184, 104", earth; by its armature 134 it switches conductor 135 from conductor.133 to conductor, 513, the importof which will be discussed later; by its armaturel34 it completes path for current through" B 140, home trunk-extension relay 53*, 154,134,

152, earth; energizing relay 53 and hold high-resistance secondary switchboard re- I lay 56 1s shunted out and releases its armature 130 this removes the earth connection from conductor 135 wlnch is common to all switchboard line equipments of the group to whichthe desired line (56) belongs, and

from conductor 141, which is. common to all switchboard line'equipments on 'the fifth level of the bank of contacts of the automatic switch of Fig. 4.

The switching of conductor 135 from conductor 133 to conductor 51 is for the purpose of transferring the next call originating 0n the switchboard and for this group of lines'to be cared for by the oper- 0 from spring 15 and making contact with spring ,13'. By the energization of home trunk-extension relay '53, the trunk conmemes 5:3

ductors are extended to the connecting plug P and path is closed for current through B, 45 145", 155, 13*, 1e, 137, 13s, con tact of 53 8*, 156, 199. J. P, 69, 70, earth, energizing distant think-extension relay 15". which then locks itself through B, 45", 1&5, resistance 158, contact of =1" and earth. By the energization of relay 15" the trunk conductors are extended to the line conductors 18 and 19 of the line desired. viz., that line leading to substation Considering that the line circuit is open at the hook switch of substation 56, the only circuit through the super isory relay 67 is B 66, 67, 68, P, J, 161, 156', 9, contact of 53, 146, contact of 415", 9,156, 17, earth, but inasmuch as the resistance of 17 is high, say 12,000 ohms, the supervisory relay 67 does not respond to-the current. The supervisory relay 67 is under control of the hook switch of the substation 56 since when that switch is closed the circuit will exist through B 66, 67-, 68, P, J, 161, 156', 9, contact of 533. 116, contact, of- 452 9", 156".

19, 5e, 18, 156 8, Contact of 138, G011- tact'of 53, 8, 156,199, J, P, 69, 70. Upon the closing of the home and distant trunkeXtension relays path is closed for current through B, 17 156 8', contact of 45?, 138, contact of 53, S 156", 199, J, P, '69, 70, earth, energizing relay 17. The closing of armature 17 efl'ects nothing. Current flows through 31 but not through 30 since one terminal of 30 is connected directly to bat tery B and the other terminalis connected through 198, 197, 156", 10, contact 6f 4:5" to battery B", these two batteries being the same or similar. The operator, having plugged into the jack .1 (the above outlined automatic action having followed quickly), now rings by the operation' of the ringing key K. While this key is operated the re lay 17 is held energized by current through B, 17, 156", 8', contact of'4c5, 138, contact of 53 8, 156, 199, J, P, 196, earth, and ringing current flows from generator G through 195, 68, P, J, 161, 156', 9*, contact of 53, 146, contact of 415., 9", 156 ,'c 0ndenser and ringer of 56, 156, 8", contact of 45 138, contact of 53 8 156', 199, J, r, 69,196.

In disconnection, the trunk isreleased by removal of the operators plug regardless of the open or closed condition of. the hook:

switch of substation 56. By withdrawal of the plug P, the circuit through relay is broken; by the release of armature 60" the I 'olf-normal switch 531 82, as described in connection with the corresponding switch of Fig. 3,

, trunks equipped with automatic switches at each end, the two switches of the two ends of the trunk operating in unison to connect any outlying line with its switchboard line equipment or rice ersa.

It will be noted that the paths, which normally lead from the subscribers jacks or connection terminals at the main switchboard, terminate in open contacts on the automatic switches which are normally con nected to nothing else. In this respect these paths may be called blind paths, in the sense, for instance, that an alley which comes to an abrupt end. and leads nowhere, is a blind alley. Similarly, the branches from the subscribers lines at the sub-oflice, which lead from the line conductors to the contacts on the switches, are blind paths leading from the subscribers lines, since normally there is no path beyond. With this in view, the following statement will. make clear one of the fundamental features of my in ention. The jacks. or connection terminals at the main office, although each of them corresponds definitely to a given subscribers line, normally are wholly dissociated from the subscribers lines, except in so far as they may bear the same designating numbers or other insignia. The paths leading from these jacks are normally blind paths. The subscribers lines which terminate at the sub-station each has a branch path leading to contacts in the automatic switches, from which contacts there is'no normal path, and these branchestherefore, are blind paths. Each of these contacts and each of these blind paths is normally physically dissociated from its correspondiiig 'jack or other connection terminal onthe distant centraloffice switchboard, the only association being that they bear corresponding numbers or other insignia. The trunks from the main ofiice to the'branch office, or subbflice, are fewer in number than the corresponding-group of lines at the suboflic'e' and fewer in' number than the corresponding group of jacks or other connection-terminals at the main ofiice; and these trunks have for their functlon theconnecting, togetl 1e1'. as required, of'any one of the blind paths leading from the switchboard terminals tothe corresponding one of the bliiid paths leading from the subscribers lines. Each of these trunks has a switching mechanism at each end, the two switching receives a call for a certain line in the sub blind path leading fromthe desired subcall originating on one of the sub-ofiice ofiice, she plugs into the jack corresponding to the line wanted, in spite of the fact that at the time that jack terminates in a blind path-which has no association with the line wanted, except that it bears the same number. The automatic switching apparatus associated with the'two ends of the first idle trunk then, in response to this act, automatically connects one end of the trunk with the blind path chosen by the operator, and the other end of the trunk with the scribersline. Similarly, with respect to a lines, the removal of the subscribers re ceiyer from its hook in making a call will establishsuch a condition that the first idle trunk will connect with-the normally blind 'at the same-time the switching the normally blind path leading from the jack which bears the corresponding subscribers number. In either case the trunk automatically supplies the connecting link between the two physically dissociated blind paths, and thus supplies the physical associating link between the line and its connec tion terminal on the switchboard where the only previously existing association had been that of number or other corresponding designation. r

I believe myself to be the first to have devised a system having this broad method of operation, by which the connecting links between a line and its correspondingly designated switchboard terminal are normally missing, the line and its switchboard termi nal being associated only by number or other corresponding insignia, and by which the connecting physical link is automatically supplied only at the time of the required connection. Obviously, asystem operating in this way is capable of use with a widevariety of telephone switching systems, and is in itself susceptible to wide variation without departure from the spirit of the broad invention as I have outlined it. In some of theclaims which follow I have used the term blind path in accordance with the meaning just defined.

Having thus described my invention, what I claim as new and desire to secure by United States Letters Patent is:

1. In a telephone system, a switchboard having a plurality of subscribers line equipments; a plurality of subscribers? lines dissociated from said switchboard, and pertaining one to each of said lineequipments; and a trunk common to all subscrlbers lines and having ends equipped with switches acting automatically to connect one of said subscribers lines to 1ts corresponding line equipment when controlled initially by one of said subscribers-line equipments, substantially-as described. p

,' 2. In a telephone system, a switchboard.

having a plurality of subscribers-line equip ments; a plurality of subscribers lines dissociated from said switchboard, and pertaining one toeach of said line equipments; and a trunk having automatic connectors at each end whereby any subscribers line may be connected through the trunk and its automatic switches to that subscribers lines switchboard equipment, substantially as described. w

3; In a telephone system, a trunk line; two selecting switches, one for each end of said trunk line; stationary contacts at said switches; and electromagnetic means for automatically moving .said two switches in unison to unite with corresponding contacts, substantially as desoribedw .1 4;. In a telephone systemfaswitchboard having a plurality of subscribers-line equipments; a plurality ofsubscriberslines dissociated from said switchboard, and pertaining one to each of said line equipments} an automatic switch forfselectingand connecting with said subscribers lines; an automatic switch for selecting and connecting with said subscribers line equipments of said switchboard; and means for causing said two automatic switches to move'in corresponding steps, substantially as described.

5. In a telephone system. a switchboard other of said switches, substantially as described.

6. In a telephone system, a switchboard having a plurality of subscribers-l'ine equipments; a plurality of subscribers lines dissociatedirom said switchboard, and pertaining one to' each of said line equipments; trunks between said switchboard equipment and said lines; means controlled by one of said lines" for causing one of said trunks to connect with said line, and further means for causing the alternative end of said trunk to connect automatically with that subscribers-line equipment of the switchboard which pertains to said subscribefis-line. substantiall as described.

7. In a telephone system, a plurality. of outlying subscribers lines: a manual switchboard: jacks .and plugs onsaid switchboard. said jacks corresponding severally to the respective subscribers lines; a. trunk; means controlled by the insertion of a plug in a jack to cause the connection of said trunk with said ack; and further means for connecting automatically the other end of said trunk with the corresponding outlying subscribers line. substantially as described.

S. In a telephone system, an automatic switch, said automatic switch having an operating magnet and a normally closed offnormal switch: an operating circuit includ ing said'operating magnet and said oft-normal switch in series. whereby the first energization of said operating magnet may be had only through said. oft-normal switch; an auxiliary operating circuit; means for making said auxiliary circuit effective only through said first operating circuit: and means for interrupting said' auxiliary in the beginning of the process of: disconnection and restoration. m

9. In a telephone system. an automatic switch; an operating circuit for said auto matic switehwhereby said switch may be actuated selectively: a main controlling circuit for said switch; a self-locking relay holding said main controlling circuit normally open when said switch is in its position of idleness; and a primary circuit for energizing said rela to close said'main controlling circuit and including the normallyclosed contacts of an off-normal switch.

1Q. In a telephone system; a switchboard having a plurality of line jacksza plurality of lines normally disconnected from'said line jacks and pertaining one toeach of said line 1acks: a pair of automatic switches. and a trunk connecting them. the automatic switch at one endbeing adapted toconnect with any line. and the automatic switch at the other end being adapted to connect with any jack; and circuits adapted to maintain said ai'it-omatic switches in analogous positions. I

11. In a telephone system, a switchboard having a plurality of line jacks; a'plurality of I lines normally disconnect-ed from said line iacks and pertaining oneto each ofsaid line jacks: a pair'ot automatic switches. and a trunk connecting them, the automatic switch at one end being adapted to'connect with any line. and: the automatic switch at the other end being-adapted to connect with any 1ack; ameans ot' control rendered active by any of said lines and acting to cause the switch contiguous to the lines to connect the trunk with the controlling line; and further means for moving said switches in unison.

19. In a telephone system, a switchboard having a plurality of line jacks; a plurality of lines normally disconnected from said line jacks and pertaining one to each of said line jacks: a pair of automatic switclurs. and a trunk connecting them, the automatic switch at one end being adapted to connect with any line. and the automatic switch at the other end being adapted to connect with any jack: a means of control rendered active by any of said lines and acting to cause the switch contiguous tothe linesto connect the trunk with the controlling line. and further means for causing the other oi said switches to take a. selective position analogdus to the first switch controlled.

13. In a telephone system. a switchboard haying a plurality of line jacks; a plurality of lines normally disconnected from said line jacks and pertaining one to each of said line jacks: a pair of automatic switches. and a trunk connecting them. the automatic switch at one end being adapted to connect withany line. and the automatic switch at the other end being adapted to connect with any "jack; said switches moving in unison.

14:. In a telephone s stem, aswitchboard having a plurality of line jacks; a plurality of lines normally disconnected from said line jacks and pertaining one to each or' said line jacks: a pair of automatic switches, and a trunk connecting them. th automatic switch at one end being adapted to connect with any line. and the automatic switch at the other end being adapted to connect with any jack;.said'switches being controlled one by the other in their movements of selection.

15. In a telephone system. a switchboard ha ring aplurality of line jacks: a plurality of lines normally disconnected from said line jacks and pertaining one to each of said line jacks; a pair of automatic switches.

and a trunk connecting them. the automatic 'switch at one end being adapted to connect with any line. and the automatic switch at the other end being adapted to connect with any iack: said switches being controlled dependently one by the other. whereby both are caused to occupyanalogous positions of selection, y

16. In a' telephone system. a switchboard having a plurality. of line jacks: a plurality of lines normally disco 'ine'cteil' from said line jacks and pertaining .one'to each of said line jacksia pair of automaticswitches. and

a trunk. connecting thenn the automatic switch at one end being adapted to connect withany" line, and the automatic switch at the other end being adapted to connectwith any jack; saidswitches beingdependently controlledone by the other. the controlling magnetsot one being included in circuits over the trunk conductors to controlling reany jack; said two automatic switches moying at all tunes in corresponding steps.

.18. In a telephone system, a switchboard having a pluralityof line jacks; a plurality of lines normally disconnected from said line jacks and pertaining one to each of said line acks; a pair of automatic switches, and a trunk connecting them, the automatic switch at one end being 'adapted to connect with any line, and the automatic switch at the other end being adapted to connect with any jack; said two automatic switches movv ing at all times in corresponding steps, and said lines and jacks being identifiable in related pairs comprising each a line and a jack by the analogous positions of the line and the jack.

19. In atelephone system, aswitchboard having a plurality of line jacks; a plurality of lines normally disconnected from said line jacks and pertaining one to each of said line jacks; a pair of automatic switches, and a trunk connecting them, the automatic switch at one end being adapted to connect with any line, and the automatic switch at.

the other end being adapted tolconnect with any jack; said two automatic switches moving at all times in corresponding steps, said lines and jacks being related in pairs and analogously located 'in said selecting switches, aud'wher'eby in all effective posi-r tions of selection, said two automatic iwitches connect a jack to its corresponding ine.

20. In a telephone system, a switchboard having a plurality of line jacks; a plurality of lines normally disconnected from said line jacks and pertaining one to each of'said line jacks; a pair of automatic switches, and a trunk connecting them, the automatic switch at one end being adapted to connect with any line, and the automatic switch at the other end bein adapted to connect with anyjack; switch p ugs for said jacks, means 'for operating the automatic switch contiguous to said jacksin responseto the insertion of a plug inZ-a ackand' to connect the trunk to the jacl rf-P'plugged into, and'further means for .m'ov'ing the two automatic switches in unison. a

21. In a telephone system, a switchboard having a, plurality 'of line jacks; a plurality of lines normally disconnected from said line jacks and pertaining one to each of said' line jacks; a pair of automatic switches, and a trunk connecting them, the automatic switch at one end being adapted to connect with any line, and the automatic switch at the other end being adapted to connect with any jack; switch plugs for said vjacks, means for operating the automatic switch contiguous to said jacks in response to the insertion of a phw in a jack and to connect the trunk to the jack plugged into, and further means for effecting analogous positions of selecti on in said two switches; automatically.

22. In a'tel'ephone system, a main office and a suh-oiiice;'a11tomatic switching apparatus at both said oflices; a group of subscribers lines terminating at said sub-office; a normally blind path from each subscribers line to said sub-oflice switching apparatus; switchboard connection terminals, one for each subscribers line at said main ollice; a normally blind path leading from each of said connection -terminals at the main oliice; a group of trunk lines connecting said ofiices, fewer in number than the blind paths'of the corresponding groups at said main oflice and .at said sub-office, and means for automatically causing the switching apparatus to connect the two ends of one trunk to the corresponding blind paths pertaining to a given subscribers line upon the origination of a call.

23. In atelephone system, a' main 'oflice and a sub-office; automatic trunk switching v apparatus at both said oflices; a group of subscribers: lines terminating at said sub ofiice; a normally blind path from each sub scribers line to said sub-office switching ap paratus; switchboard connection terminals, one for each subscribers line at said main oliice, a normally blind path leading from each ofsaid connection terminals at the main oflice; a group of trunk lines connecting said oflices, fewer in number than the corresponding groups of blind paths at said main office and at said sub'-o1fice; means for automatically causing the main and suboliice switching apparatus to connect the two ends of one trunk to the corresponding blind paths pertaining to a given subscribers'line upon the origination of a call, and means for guarding said trunk and said blindpaths from other connections during "the existence of an established connection.

24. In a telephone system, amain oifice and a sub-oihce,' switching apparatus at both said oilices; a group of subscriberslmes terminating at said sub-office; a group of connection terminals at said main office, each connection terminal of said group per- 'taining to a corresponding individual line in said group of lines, but normally physi cally dissociated therefrom; a normally blind path'from e'aeh subscribers line to said sub-oifice switching apparatus; a normatinee mally blind path leading from each connec- I ber than the corresponding groups of connection terminals and lines, and means for causing the main and sub-oiiice switching apparatus automatically to connect one end of each trunk to the blind path of a line at the'sub-ofiice and the other end to the blind path of a corresponding connection terminal at the main oflice upon the origination of a call at one end of said trunk line.

25. In a telephone system, a trunk line; an automatic selecting switch at each end of said trunk line; a group of paths terminating in each of said switches, and means for automatically movin' said two switches in unison to connect t e two ends of said trunk line to' corresponding ones of said paths.

26. In a telephone system, a subscribers line; a switchboard terminal individual to that line, but physically dissociated there-- from; a connecting link common to a groupof such lines and terminals, and automatic means responsive when a call is originated at. one end of said connectlng link for s1- multaneously applying the ends of said connecting link to said line and terminal.

27. In a'telephone system, a gro p of sub:

scribers lines; a group of switch oard terminals dissociated therefrom; a group of incoming trunks; switches at each end of said trunks for automatically connecting a subscribers line to its corresponding switchboard terminal; another group of snbscrib ers lines; another group of; switchboardterminals dissociated therefrom; an outgoing trunk; switches at each'end of each outgoing trunk for automatically connecting one of said lines to the corresponding one of said switchboard terminals, and means for establishing a connection between said switchboard terminal so connected' for completing the circuit between said subscribers lines. 28. In a telephone system .the combination with subscribers lines, and an interconnecting switchboard therefor having 1 switchboard lines, one for each subscribers line, of trunk lines external to said switchboard and less in number'than the number of the subscriberslines, and automatic means responsive when' any of said subscribers is calling 'for connecting said subscribers line through an idle one of said trunk lines to its corresponding exchange line.

29. In a telephone system the combination with a group of subscribers lines, and

an interconnecting switchboard having switchboard lines, one for each 'subscribers line of the said group, of a trunk line external to said switchboard, and automatic means responsive when any of said subscribers is calling for connecting said subscribers line through the said trunk line to its corresponding switchboard line.

30. In a'multi-oflice telephone system the combination with a plurality of lines terminating. at one office, an automatic line finder at said oifice, a switch associated with one of said lines, and means responsive to the operation of said switch to start said line finder in search of said line, of a circuit' between said oiiices, and means at the other of said offices controlled over said circuit'to measure the movement of said line finder.

31. In a telephone system, a circuit, a pair of remote switches having electrically associated traveling contacts included in series in said circuit, assive contacts for each switch, means dr causing one of said switches toseek out and connect with a particular passive contact, means for caustwo selecting switches, one for each end of said trunk line; contacts ,for said switches, lines terminating in said contacts; and electromagnetic means actuated when a call is established on one of said lines for automatically moving said switches in.

unison to cause one switch to unite with the terminals of the line upon which the call is established and the other switch to unite with the corresponding terminals thereat.

Si ed by me at Ghicago,.county of Cook and tate of Illinois, in the presence of two witnesses.

- EDGARII. CLARK. Witnesses: .DAVID S. HULFISH,

Guanine I. Conn.

85 mg the other switch to move in synchronism 

